Cinematograph apparatus



K. HIGGINSON.

CINEMATOGRAPH APPARATUS.

FILED JULY 2|. 192! Feb. 13, 1923,

Patented Feb. 13, 1923.

UNITED STATES PATENT OFFICE.

KINGSLEY HIGGINSON, F KINGSTON-ON-THAMES, ENGLAND, ASSIGNOR TO CAREY- GAVEY SYNDICATE LIMITED, OF LONDON, ENGLAND, A BRITISH LIMITED LIA- BILITY COMPANY.

CINEMATOGRAPH APPARATUS.

Application filed July 21,

To a]? whom-it may concern Be it known that I, KINosLEY HIooINsoN, a subject of the King of England, residing in Kingston-on-Thames, Surrey, England,

5 have invented certain new and useful Improvements in Cinematograph Apparatus, of which the following is a specification.

This invention relates to cinematograph apparatus, primarily to projecting apparatus, but also to apparatus for taking clnematographic photographs. The type of apparatus to which this invention relates is that in which a substantially annular mirror is employed, arranged to rotate about an axis normal to the general plane of the mirror.

the mirror itself having its reflecting surface composed of a number of trapezoidal facets inclined to the axis of rotation so as to form substantially a frustum of a manysided pyramid.

The object of this invention is to enable the distortion at the lateral edges of the pictures upon the screen to be reduced to a value sufficiently small to be tolerable to the observer, or at least to a value less than has heretofore been obtained, the said lateral distortion being an important factor in preventing successful operation of apparatus of the type described.

The present invention provides cinematograph apparatus of the type described characterized by the inclination of each trapezoidal facet to the axis of rotation of the annular mirror being made not substantially greater than is just sufficient to permit the projection beam received by a facet through one open side of the annulus along a direc tion in which the beam just clears the ed e of the annulus opposite to the facet to be thereby reflected through the other open side of the annulus in a direction in which it just'clears the edge of that side.

Preferably, according to this invention, the projection beam entering the said annulus is arranged to be a divergent beam.

In constructions heretofore proposed for apparatus of this general type. the annular mirror has been supported and/or driven entirely from means arranged external to its own periphery but experiment has shown that spokes may be employed extending inwards from the periphery without undue in- 1921. Serial No. 486,454.

terference with the projection of the pictures. A construction having such spokes 1s conduclve to ease and economy of construction and is otherwise advantageous. for example they may serve to transmit the drivmg effort.

The nature of this invention and the manner in which it is to be performed is further disclosed by reference to the accompanying drawings, in which Flgure l is a diagrammatic plan of an ap paratus embodying this invention; 1

Figure 2 is a diagram showing the annular mirror in section, and

F1gure 3 is a diagrammatic plan similar to a portion of Figure 1 showing a modification. V In Figure 1 of the drawings, the pro- JEftOI' is indicated at 1 and the annular mirror at 2.

Bearings are arranged externally at 5 and driving effort to rotate the mirror is applied to the external periphery as indicated at 6. It will be obvious that whatever means to rotate the mirror are employed. they must be of such a character as will enable s-y'nchronism to be maintained between the movement of the film in the gate and that of the facets across the projection beam. The means employed for this purpose. form no part of the present invention and are not shown in the drawings.

The mirror is mounted to rotate about a horizontal axis, and with its general plane slightly inclined to the optical axis of the projector and its projecting lens. The parts are so disposed that the beam 8 enters one open side of the mirror at such a small inclination to the general plane of the latter as just to clear the nearer edge of the mirror at 9 and impinge fully upon a diametrically opposite facet at 10.

The disposition of the facetsof the mirror with regard to the axis of rotation of the latter. and the direction of the projection beam before and after reflection are more clearly shown in Figure 2. The angular inclination of the facet ll) to the axis of rotation 11 of the mirror is such that the reflected beam emerges at 12 through the other side of the mirror from that by which it enters. at such a small inclination to the general plane of the latter as just to clear the edge of the mirror. The entering and emerging beams at 8 and 12 therefore are separated from one another, at the point where they embrace the mirror, by a distance that is only slightly greater than the depth of the mirror measured in the direction of its axis of rotation.

ltt will be seen that with the arrangement One of the hubs may have rotative effort applied to it.

Such a construction is indicated diagrammatically in Figure 3 where, however, only one hub is provided as seen-at 14; spokes are shown at 15. The hub carries a sprocket.

wheel .16 by which it may be driven, care being taken to lead the driving chain in a direction which will not interfere with the passage of the projection beam. Any convenient means may be adopted, obviously, for driving the hub. The number of spokes may be varied as desired, but is such preferably as to give a spacing by which no spoke is in the direct path of the beam when the parts are in such a position that the screen is being illuminated entirely by the reflection at a single facet of the mirror.

What I claim as my invention and desire to secure by Letters Patent is Tn cinem atograph apparatus the combination of a projection lens, a screen, and a rotating annular mirror provided withspokes extending radially from the periphery to a central hub and which is located optically between the said lens and screen and comprises a band of trapezoidal reflecting facets each so inclined to the axis of rotation of the mirror that the reflecting surface of the mirror. conforms to a frustum of a pyramid, which said mirror is so located and has its facets so inclined that a beam, projected from said lens to enter the mirror through one open side thereof and fall upon a facet at such an angle with the general plane of rotation of the mirror that said beam just clears the part of the mirror lying near its path between the lens and said facet, completely fills the said facet between its mutually inclined edges and is reflected out through theother open side of the mirror at such an angle with respect to the said plane of rotation that the beam just clears the part of the mirror lying near its path between the said facet and the screen, and which said spokes are so disposed that when the incident and reflected beams are contained in a. plane containing the axis of rotation of the mirror no spoke shall intercept the said beams, substantially as described. I

In testimony whereof I afiix my signature.

KTNGSLEY HIGGINSON. 

